Hydraulic device such as an oil pump and a hydraulic actuator will be explained as an example of background of the present invention. For these hydraulic devices, a tool steel (e.g. SKH51, etc.) has been frequently used as a vane material. The main purpose of the vane is as follows. Namely, in the case of an oil pump, function of a pump is achieved by pushing out of oil filed in a cavity formed between a housing and the vane using the vane via driveshaft. On the other hand, in the case of a vane type hydraulic actuator, required function is achieved by driving a driveshaft fixed to a vane which is actuated by taking oil in and out in a cavity formed between a housing and the vane.
Mechanical properties required to the vane are strength to bear with required oil pressure, especially bending strength and fatigue strength, and abrasion resistance against sliding between the vane and the housing or the other members surrounding the vane.
In recent internal combustion engine, hard carbon soot tends to increase in lubricating oil since fuel supply system has been alternated to direct injection type and so on. Abrasion resistance against hard carbon soot floating in the oil has been required for the vane with the exception of abrasion resistance against surrounding members with relative motion.
In addition, abrasion resistance has been required for the other hard particles such as fine silica (generally 0.2 mm or less) which is floating in oil by entering in unavoidable condition of device using and production.
Another example is disclosed in Japanese Patent Publication published as Toku-Kou-Hei 1 (1989)-18985. This rotational fluid compressor includes a vane and an opposed member. The vane is made of a steel system material which includes 0.50–1.30 weight % of carbon, 11.0–20.0 weight % of chromium and iron with hardening, tempering and nitrocarburizing treatment. And the opposed member made of a cast iron, which includes 0.10–6.00% of carbide and have a graphite shape of A, B, D, and E in ASTM standard with HRC 40–55 in hardness.
Another example is disclosed in Japanese Patent Laid-Open Publication No. H5-78792. This rotational fluid compressor includes a vane and an opposed member. The vane is made of a steel system material which includes 0.50–1.30 weight % of carbon, 11.0–20.0 weight % of chromium and iron with hardening, tempering and ion nitriding treatment. And the opposed member made of a cast iron, which includes 0.10–6.00% of carbide and have a graphite shape of A, B, D, and E in ASTM standard with HRC 40–60 in hardness.
According to the above described vane made of iron system material typified by SKH51, carbon content included in the steel exceeds 0.85 weight %. Then, carbide such as Fe3C is generated in the vane body matrix. This compound can improve abrasive resistance of the vane.
However, additional improvement of slidability of the vane has been required in these years. For example, frequency of oil change by user is getting decrease since engine parts and so on are changed to have high performance in these years. Under this condition, carbon soot and silica hard particles floating in the oil contribute to generation of erosion and abrasion in high speed flow. Accordingly, only soft portion of the vane body matrix has a tendency to abrade away, thus carbide which is hard particles (such as Fe3C) has a tendency to be exposed at the surface of the vane. Therefore, the vane has a tendency to attack the surface of the opposed member such as a housing and a rotor.